(1) Field of the Invention
The present invention relates to an electro-oculography measuring device that can output an electro-oculography signal by removing noise from an electro-oculography original signal.
(2) Description of the Related Art
The present invention relates to a noise reduction device and method for reducing noise that occurs when measuring an electro-oculogram of a human.
In recent years, EOG that utilizes a potential generated between a cornea and a retina has been proposed as a method for detecting an eye movement of a human.
EOG mentioned here is an eye movement detection method based on the fact that the human cornea is charged positively with respect to the retina. In detail, electrodes are placed near a human eyeball, and an eye movement is detected from a change in potential measured from the electrodes. FIGS. 63A and 63B show an example of the eye movement detection method employing EOG. The case where the electrodes are placed at two positions that are to the right and left of the right eye of the user at the same distance away from the center of the eyeball is shown as an example.
Let Va be an electro-oculogram generated on an electrode A placed to the right, and Vb be an electro-oculogram generated on an electrode B placed to the left. When the eyeball of the user is positioned at the center as shown in FIG. 63A, Va and Vb are equal, so that a measured electro-oculogram Va-b is 0 V. On the other hand, when the user looks to the right as shown in FIG. 63B, the electrode A is closer to the cornea of the right eye and accordingly Va>Vb, so that the measured electro-oculogram Va-b is a plus value. Conversely, when the user looks to the left, Va<Vb, so that the measured electro-oculogram Va-b is a minus value. That is, the plus value of the measured electro-oculogram Va-b indicates that the user has moved the eye to the right, and the minus value of the measured electro-oculogram Va-b indicates that the user has moved the eye to the left. In EOG, the user's eye movement is detected by utilizing such a change in measured electro-oculogram Va-b.
When detecting the eye movement using EOG in this way, noise included in a generated electro-oculography signal needs to be reduced in order to increase detection accuracy. As an example of a noise reduction method, the following technique is described in Patent Literature 1.
In the noise reduction method disclosed in Patent Literature 1, first the user is instructed to gaze at a specified position, and an electro-oculography signal during this time is measured. Such an electro-oculography signal in a state where eye movements are intentionally reduced is treated as drift noise. In subsequent measurement, a signal corresponding to the drift noise is subtracted from a measured electro-oculography signal.